WELDING

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Welding is any metal joining process wherein coalescence is produced by heating the metal to suitable temperatures, with or without the application of pressure and with or without the use of filler metals.

METAL TYPE:

The metals that steelworkers work with are divided into two general classifications: ferrous and nonferrous. Ferrous metals are those composed primarily of iron and iron alloys. Nonferrous metals are those composed primarily of some element or elements other than iron. Nonferrous metals or alloys sometimes contain a small amount of iron as an alloying element or as an impurity.FERROUS METALS

Ferrous metals include all forms of iron and steel alloys. A few examples include wrought iron, cast iron, carbon steels, alloy steels, and tool steels. Ferrous metals are iron-base alloys with small percentages of carbon and other elements added to achieve desirable properties. Normally, ferrous metals are magnetic and nonferrous metals are nonmagnetic.

IronPure iron rarely exists outside of the laboratory. Iron is produced by reducing iron ore to pig iron through the use of a blast furnace. From pig iron many other types of iron and steel are produced by the addition or deletion of carbon and alloys. The following paragraphs discuss the different types of iron and steel that can be made from iron ore.

PIG IRON.— Pig iron is composed of about 93% iron, from 3% to 5% carbon, and various amounts of other elements. Pig iron is comparatively weak and brittle; therefore, it has a limited use and approximately ninety percent produced is refined to produce steel. Cast-iron pipe and some fittings and valves are manufactured from pig iron.

WROUGHT IRON.— Wrought iron is made from pig iron with some slag mixed in during manufacture. Almost pure iron, the presence of slag enables wrought iron to resist corrosion and oxidation. The chemical analyses of wrought iron and mild steel are just about the same. The difference comes from the properties controlled during the manufacturing process. Wrought iron can be gas and arc welded, machined, plated, and easily formed; however, it has a low hardness and low-fatigue strength.

CAST IRON. — Cast iron is any iron containing greater than 2% carbon alloy. Cast iron has a high-compressive strength and good wear resistance; however, it lacks ductility, malleability, and impact strength. Alloying it with nickel, chromium, molybdenum, silicon, or vanadium improves toughness, tensile strength, and hardness. A malleable cast iron is produced through a easily as the low-carbon steels. They are used for crane prolonged annealing process hooks, axles, shafts, setscrews, and so on.

INGOT IRON. — Ingot iron is a commercially pure iron (99.85% iron) that is easily formed and possesses good ductility and corrosion resistance. The chemical analysis and properties of this iron and the lowest carbon steel are practically the same. The lowest carbon steel, known as dead-soft, has about 0.06% more carbon than ingot iron. In iron the carbon content is considered an impurity and in steel it is considered an alloying element. The primary use for ingot iron is for galvanized and enamelled sheet.

SteelOf all the different metals and materials that we use in our trade, steel is by far the most important. When steel was developed, it revolutionized the American iron industry. With it came skyscrapers, stronger and longer bridges, and railroad tracks that did not collapse. Steel is manufactured from pig iron by decreasing the amount of carbon and other impurities and adding specific amounts of alloying elements.

Do not confuse steel with the two general classes of iron: cast iron (greater than 2% carbon) and pure iron (less than 0.15% carbon). In steel manufacturing, con-trolled amounts of alloying elements are added during the molten stage to produce the desired composition. The composition of a steel is determined by its application and the specifications that were developed by the following: American Society for Testing and Materials (ASTM), the American Society of Mechanical Engineers (ASME), the Society of Automotive Engineers (SAE), and the American Iron and Steel Institute (AISI)

Carbon steel is a term applied to a broad range of steel that falls between the commercially pure ingot iron and the cast irons. This range of carbon steel may be classified into four groups:

AluminumPure aluminum is a silvery-white metal with many desirable characteristics. It is light, nontoxic (as the metal), nonmagnetic and nonsparking. It is easily formed, machined, and cast. Pure aluminum is soft and lacks strength, but alloys with small amounts of copper, magnesium, silicon, manganese, and other elements have very useful properties. Aluminum is an abundant element in the earth's crust, but it is not found free in nature. The Bayer process is used to refine aluminum from bauxite, an aluminum ore. Because of aluminum's mechanical and physical properties, it is an extremely convenient and widely used metal.Properties -

very lightweight (about 1/3 the mass of an equivalent volume of steel or copper) but with alloying can become very strong.

excellent thermal conductor

excellent electrical conductor (on a weight-for-mass basis, aluminum will conduct more than twice as much electricity as copper)

highly reflective to radiant energy in the electromagnetic spectrum

highly corrosion resistant in air and water (including sea water)

highly workable and can be formed into almost any structural shape

non-magnetic

non-toxic

BerylliumBeryllium has one of the highest melting points of the light metals. The modulus of elasticity of beryllium is approximately 1/3 greater than that of steel. It has excellent thermal conductivity, is nonmagnetic and resists attack by concentrated nitric acid. It is highly permeable to X-rays, and neutrons are liberated when it is hit by alpha particles, as from radium or polonium (about 30 neutrons/million alpha particles). At standard temperature and pressures beryllium resists oxidation when exposed to air (although its ability to scratch glass is probably due to the formation of a thin layer of the oxide). Beryllium is a very light weight metal with a high modulus of elasticity (five times that of ultrahigh-strength steels), high specific heat, and high specific strength (strength to weight ratio).Uses -Beryllium is used as an alloying agent in the production of beryllium-copper because of its ability to absorb large amounts of heat. Beryllium-copper alloys are used in a wide variety of applications because of their electrical and thermal conductivity, high strength and hardness, nonmagnetic properties, along with good corrosion and fatigue resistance. These applications include the making of spot-welding electrodes, springs, non-sparking tools and electrical contacts.Due to their stiffness, light weight, and dimensional stability over a wide temperature range, beryllium-copper alloys are also used in the defense and aerospace industries as light-weight structural materials in high-speed aircraft, missiles, space vehicles and communication satellites.

Thin sheets of beryllium foil are used with X-ray detection diagnostics to filter out visible light and allow only X-rays to be detected.

In the field of X-ray lithography beryllium is used for the reproduction of microscopic integrated circuits. Because it has a low thermal neutron absorption cross section, the nuclear power industry uses this metal in nuclear reactors as a neutron reflector and moderator.

Beryllium is used in nuclear weapons for similar reasons. For example, the critical mass of a plutonium sphere is significantly reduced if the plutonium is surrounded by a beryllium shell.

It is, however, brittle, chemically reactive, expensive to refine and form, and its impact strength is low compared to values for most other metals.CopperCopper provides a diverse range of properties: good thermal and electrical conductivity, corrosion resistance, ease of forming, ease of joining, and color. However, copper and its alloys have relatively low strength-to-weight ratios and low strengths at elevated temperatures. Some copper alloys are also susceptible to stress-corrosion cracking unless they are stress relieved. Next to silver, copper is the next best electrical conductor. It is a yellowish red metal that polishes to a bright metallic luster. It is tough, ductile and malleable. Copper has a disagreeable taste and a peculiar smell. Copper is resistant to corrosion in most atmospheres including marine and industrial environments. It is corroded by oxidizing acids, halogens, sulphides and ammonia based solutions.Copper and its alloys -- the brasses and bronzes -- are available in rod, plate, strip, sheet, tube shapes, forgings, wire, and castings.LeadLead is the most impervious of all common metals to X-rays and gamma radiation and it resists attack by many corrosive chemicals, most types of soil, and marine and industrial environments. Main reasons for using lead often include low melting temperature, ease of casting and forming, high density, good sound and vibration absorption, and ease of salvaging from scrap. Sheet lead, lead-loaded vinyls, lead composites, and lead-containing laminates are used to reduce machinery noise. The natural lubricity and wear resistance of lead make the metal suitable, in alloys, for heavy-duty bearing applications such as railroad-car journal bearings and piston-engine crank bearings.

PLASMA CUTTING

ARC / STICK WELDING

Magnesium

As the lightest structural metal available, magnesium has a high strength-to-weight ratio. With its low modulus of elasticity combined with moderate strength, magnesium alloys can absorb energy elastically, providing excellent dent resistance and high damping capacity. Magnesium has good fatigue resistance and performs particularly well in applications involving a large number of cycles at relatively low stress. The metal is sensitive to stress concentration, however, so notches, sharp corners, and abrupt section changes should be avoided. Magnesium alloys are the easiest of the structural metals to machine and they can be shaped and fabricated by most metalworking processes, including welding.

Nickel

Nickel fits many applications that require specific corrosion resistance or elevated temperature strength. Some nickel alloys are among the toughest structural materials known. When compared to steel, other nickel alloys have ultrahigh strength, high proportional limits, and high moduli of elasticity. Commercially pure nickel has good electrical, magnetic, and magneto-restrictive properties.

Precious Metals

Gold is an extremely inert, soft, ductile metal, that undergoes very little work hardening. A gram of pure gold can be worked into leaf covering 6 ft^2 and only 0.0000033 in. thick. It is used chiefly for linings or electrodeposits and is often alloyed with other metals such as copper or nickel to increase strength or hardness.

Silver is a very malleable, ductile, and corrosion resistant metal that has the highest thermal and electrical conductivity of all metals and is the least costly of all the precious metals. Alloyed with copper, and sometimes with zinc, silver is also used in high-melting temperature solders.

Platinum is an extremely malleable, ductile, and corrosion resistant silver-white metal. When heated to redness, it softens and is easily worked. It is nearly nonoxidizable and is soluble only in liquids that generate free chlorine such as aqua regia. Because platinum is inert and stable, even at high temperatures, the metal is used for high-temperature handling of high-purity chemicals and laboratory materials. Other applications include electrical contacts, resistance wire, thermocouples, and standard weights.

Refractory Metals

Refractory metals are characterized by their extremely high melting points, which range well above those of iron, cobalt, and nickel. They are used in demanding applications requiring high-temperature strength and corrosion resistance. The most extensively used of these metals are tungsten, tantalum, molybdenum, and columbium (niobium).

Tin

Tin is characterized by a low-melting point (450°F), fluidity when molten, readiness to form alloys with other metals, relative softness, and good formability. The metal is nontoxic, solderable, and has a high boiling point. The temperature range between melting and boiling points exceeds that for nearly all other metals (which facilitates casting). Upon severe deformation, tin and tin-rich alloys work soften. Principal uses for tin are as a constituent of solder and as a coating for steel (tinplate, or terneplate). Tin is also used in bronze, pewter, and bearing alloys.

Titanium

There are three structural types of titanium alloys:

Alpha Alloys are non-heat treatable and are generally very weld- able. They have low to medium strength, good notch toughness, reasonably good ductility and possess excellent mechanical properties at cryogenic temperatures. The more highly alloyed alpha and near-alpha alloys offer optimum high temperature creep strength and oxidation resistance as well.

Alpha-Beta Alloys are heat treatable and most are weldable. Their strength levels are medium to high. Their hot-forming qualities are good, but the high temperature creep strength is not as good as in most alpha alloys.

Beta or near-beta alloys are readily heat treatable, generally weldable, capable of high strengths and good creep resistance to intermediate temperatures. Excellent formability can be expected of the beta alloys in the solution treated condition. Beta-type alloys have good combinations of properties in sheet, heavy sections, fasteners and spring applications.

ZincZinc, a crystalline metal with moderate strength and ductility, is seldom used alone except as a coating. In addition to its metal and alloy forms, zinc also extends the life of other materials such as steel (by hot dipping or electrogalvanizing), rubber and plastics (as an aging inhibitor), and wood (in paints). Zinc is also used to make brass, bronze, and die-casting alloys in plate, strip, and coil; foundry alloys; superplastic zinc; and activators and stabilizers for plastics.

Uses -

One of the most useful characteristics of zinc is its resistance to atmospheric corrosion, and just over half of its use is for the protection of steelwork. In addition to its metal and alloy forms, zinc also extends the life of other materials such as steel (by hot dipping or electrogalvanizing), rubber and plastics (as an aging inhibitor), and wood (in paints). Zinc is also used to make brass, bronze, and die-casting alloys in plate, strip, and coil; foundry alloys; superplastic zinc; and activators and stabilizers for plastics.

ZirconiumRelatively few metals besides zirconium can be used in chemical processes requiring alternate contact with strong acids and alkalis. Major uses for zirconium and its alloys are as a construction material in the chemical-processing industry.

MIG CO2 WELDING IN POSITION

BASIC QUESTIONS & ANSWERS :

1. What is Arc Welding?Arc welding is a method of joining two pieces of metal into one solid piece. To do this, the heat of an electric arc is concentrated on the edges of two pieces of metal to be joined. The metal melts, while the edges are still molten, additional melted metal is added. This molten mass then cools and solidifies into one solid piece.2. What is a Stick Electrode? A short stick of welding filler metal consisting of a core of bare electrode covered by chemical or metallic materials that provide shielding of the welding arc against the surrounding air. It also completes the electrical circuit, thereby creating the arc. (Also known as SMAW, or Stick Metal Arc Welding.)3. What is a MIG Wire? Like a stick electrode, MIG wire completes the electrical circuit creating the arc, but it is continually fed through a welding gun from a spool or drum. MIG wire is a solid, non-coated wire and receives shielding from a mixture of gases. (Process is also known as GMAW, or Gas Metal Arc Welding.)MIG wire group is devided between:1.Gas Less wire- no gas applicable /CO2 or MIX 25%ARGON + 75% CO2/-results of welding with GasLess wire is increased spatter and fume/smoke duting a welding2.FluxCored wire - /GAS ASSISTED/ for welding if proces need in short period of time to apply ticker weldin layer3.Hard Core wire - /GAS ASSISTED/ coppar plated for mild steel or just stainles steel wire4. What is a Cored Wire (Flux-Cored Wire)? Cored wire is similar to MIG wire in that it is spooled filler metal for continuous welding. However, Cored wire is not solid, but contains flux internally (chemical & metallic materials) that provides shielding. Gas is often not required for shielding. (Process is also known as FCAW, or Flux-Cored Arc Welding.)5. What is Submerged Arc? A bare metal wire is used in conjunction with a separate flux. Flux is a granular composition of chemical and metallic materials that shields the arc. The actual point of metal fusion, and the arc, is submerged within the flux. (Process is also known as SAW, or Submerged Arc Welding.)6. What is a Stick Welder? Heating the coated stick electrode and the base metal with an arc creates fusion of metals. An AC and/or DC electrical current is produced by this machine to create the heat needed. An electrode holder handles stick electrodes and a ground clamp completes the circuit.7. What is a TIG Welder? A less intense current produces a finer, more aesthetically pleasing weld appearance. A tungsten electrode (non-consumable) is used to carry the arc to the workpiece. Filler metals are sometimes supplied with a separate electrode. Gas is used for shielding. (Process is also known as GTAW, or Gas Tungsten Arc Welding.)8. What are MIG and Multi-Process Welders? Constant Voltage and Constant Current welders are used for MIG welding and are a semi-automated process when used in conjunction with a wire feeder. Wire is fed through a gun to the weld-joint as long as the trigger is depressed. This process is easier to operate than stick welding and provides higher productivity levels. CC/CV welders operate similarily to CC (MIG) welders except that they possess multi-process capabilities - meaning that they are capable of performing flux-cored, stick and even TIG processes as well as MIG.9. What is a Wire Feeder? For MIG welding or Flux-Cored wire welding, wire feeder welders are usually complete and portable welding kits. A small built in wire feeder guides wire through the gun to the piece.10. What is a Semiautomatic Wire Feeder? For MIG welding or Flux-Cored welding, semiautomatic wire feeders are connected to a welding power source and are used to feed a spool of wire through the welding gun. Wire is only fed when the trigger is depressed. These units are portable.11. What is an Automatic Wire Feeder? For MIG, Flux-Cored, or submerged arc welding, automatic wire feeders feed a spool of wire at a constant rate to the weld joint. They are usually mounted onto a fixture in a factory/industrial setting and are used in conjunction with a separate power source Gas Tungsten Arc Welding (GTAW) is frequently referred to as TIG welding. TIG welding is a commonly used high quality welding process. TIG welding has become a popular choice of welding processes when high quality, precision welding is required. Tig weld - GTAW Welding

In TIG welding an arc is formed between a non-consumable tungsten electrode and the metal being welded. Gas is fed through the torch to shield the electrode and molten weld pool. If filler wire is used, it is added to the weld pool separately. TIG Welding Benefits Superior quality welds Welds can be made with or without filler metal Precise control of welding variables (heat) Free of spatter Low distortionShielding GasesArgon Argon + Hydrogen Argon/HeliumHelium is generally added to increase heat input (increase welding speed or weld penetration). Hydrogen will result in cleaner looking welds and also increase heat input, however, Hydrogen may promote porosity or hydrogen cracking.GTAW Welding LimitationsRequires greater welder dexterity than MIG or stick welding Lower deposition rates More costly for welding thick sections

Shielded Metal Arc Welding (SMAW) is frequently referred to as stick or covered electrode welding. Stick welding is among the most widely used welding processes.

The flux covering the electrode melts during welding. This forms the gas and slag to shield the arc and molten weld pool. The slag must be chipped off the weld bead after welding. The flux also provides a method of adding scavengers, deoxidizers, and alloying elements to the weld metal.

Cracks Porosity Slag UndercutSubmerged Arc Welding ProblemsSolidification Cracking Hydrogen Cracking Incomplete fusion Irregular wire feed PorosityResistance Welding Resistance Spot Welding (RSW), Resistance Seam Welding (RSEW), and Projection Welding (PW) are commonly used resistance welding processes. Resistance welding uses the application of electric current and mechanical pressure to create a weld between two pieces of metal. Weld electrodes conduct the electric current to the two pieces of metal as they are forged together.The welding cycle must first develop sufficient heat to raise a small volume of metal to the molten state. This metal then cools while under pressure until it has adequate strength to hold the parts together. The current density and pressure must be sufficient to produce a weld nugget, but not so high as to expel molten metal from the weld zone. Resistance Welding BenefitsHigh speed weldingEasily automatedSuitable for high rate productionEconomicalResistance Welding LimitationsInitial equipment costsLower tensile and fatigue strengthsLap joints add weight and materialCommon Resistance Welding Concerns We can help optimize your welding process variables. Evaluate your current welding parameters and techniques. Help eliminate common welding problems and discontinuities such as those listed below:Resistance Welding Problems and Discontinuities Cracks,Electrode deposit on work,Porosity or cavities,Pin holes,Deep electrode indentation,Improper weld penetration,Surface appearance,Weld size,Irregular shaped weldsElectron Beam WeldingElectron Beam Welding (EBW) is a fusion joining process that produces a weld by impinging a beam of high energy electrons to heat the weld joint. Electrons are elementary atomic particles characterized by a negative charge and an extremely small mass. Raising electrons to a high energy state by accelerating them to roughly 30 to 70 percent of the speed of light provides the energy to heat the weld. An EBW gun functions similarly to a TV picture tube. The major difference is that a TV picture tube continuously scans the surface of a luminescent screen using a low intensity electron beam to produce a picture. An EBW gun uses a high intensity electron beam to target a weld joint. The weld joint converts the electron beam to the heat input required to make a fusion weld. The electron beam is always generated in a high vacuum. The use of specially designed orifices separating a series of chambers at various levels of vacuum permits welding in medium and nonvacuum conditions. Although, high vacuum welding will provide maximum purity and high depth to width ratio welds.EBW Benefits Single pass welding of thick joints Hermetic seals of components retaining a vacuumLow distortionLow contamination in vacuumWeld zone is narrowHeat affected zone is narrowDissimilar metal welds of some metalsUses no filler metalEBW LimitationsHigh equipment cost Work chamber size constraintsTime delay when welding in vacuum High weld preparation costs X-rays produced during welding Rapid solidification rates can cause cracking in some materials Common EBW Concerns We can help optimize your welding process variables. Evaluate your current welding parameters and techniques. Help eliminate common welding problems and discontinuities such as those listed below: EBW Problems and Discontinuities:Undercutting,Porosity,Cracking,Under-fill,Lack of fusion,Shrinkage voids,Missed jointsRobotic Welding There are two popular types of industrial welding robots. The two are articulating robots and rectilinear robots. Robotics control the movement of a rotating wrist in space. A description of some of these welding robots are described below:Rectilinear robots move in line in any of three axes (X, Y, Z). In addition to linear movement of the robot along axes there is a wrist attached to the robot to allow rotational movement. This creates a robotic working zone that is box shaped. Articulating robots employ arms and rotating joints. These robots move like a human arm with a rotating wrist at the end. This creates an irregularly shaped robotic working zone.There are many factors that need to be considered when setting up a robotic welding facility. Robotic welding needs to be engineered differently than manual welding. Some of the consideration for a robotic welding facility are listed below:Accuracy and repeatability Number of axes Reliability Fixtures Programming Seam tracking systemsMaintenance Controls Weld monitors Arc welding equipment Positioners Part transfer A robotic welding system may perform more repeat ably than a manual welder because of the monotony of the task. However, robots may necessitate regular recalibration or reprogramming. Robots should have the number of axes necessary to permit the proper range of motion. The robot arm should be able to approach the work from multiple angles. Robotic welding systems are able to operate continuously, provided appropriate maintenance procedures are adhered to. Continuous production line interruptions can be minimized with proper robotic system design. Planning for the following contingencies needs to be completed: Rapid substitution of the inoperable robots. Installing backup robots in the production line Redistributing the welding of broken robots to functioning robots close bySoldering and BrazingSoldering and Brazing are joining processes where parts are joined without melting the base metals. Soldering filler metals melt below 840 °F. Brazing filler metals melt above 840 °F. Soldering is commonly used for electrical connection or mechanical joints, but brazing is only used for mechanical joints due to the high temperatures involved. Soldering and Brazing BenefitsEconomical for complex assemblies Joints require little or no finishing Excellent for joining dissimilar metals Little distortion, low residual stresses Metallurgical bond is formed Sound electrical component connectionsSoldering and Brazing Issues We can help optimize your joining process variables. Evaluate your current joining parameters and techniques. Help eliminate common joining problems and discontinuities such as those listed below: Soldering and Brazing Joining Problems No wetting Excessive wetting Flux entrapment Lack of fill (voids, porosity) Unsatisfactory surface appearance Base metal erosionDISTORTION Welding involves highly localized heating of the metal being joined together. The temperature distribution in the weldment is therefore nonuniform. Normally, the weld metal and the heat affected zone (HAZ) are at temperatures substantially above that of the unaffected base metal. Upon cooling, the weld pool solidifies and shrinks, exerting stresses on the surrounding weld metal and HAZ. If the stresses produced from thermal expansion and contraction exceed the yield strength of the parent metal, localized plastic deformation of the metal occurs. Plastic deformation results in lasting change in the component dimensions and distorts the structure. This causes distortion of weldments.Several types of distortion are listed below: Longitudinal shrinkage Transverse shrinkage Angular distortion Bowing Buckling TwistingFactors affecting distortionIf a component were uniformly heated and cooled distortion would be minimized. However, welding locally heats a component and the adjacent cold metal restrains the heated material. This generates stresses greater than yield stress causing permanent distortion of the component. Some of the factors affecting the distortion are listed below:Amount of restraint Welding procedure Parent metal properties Weld joint design Part fit up Restraint can be used to minimize distortion. Components welded without any external restraint are free to move or distort in response to stresses from welding. It is not unusual for many shops to clamp or restrain components to be welded in some manner to prevent movement and distortion. This restraint does result in higher residual stresses in the components.Welding procedure impacts the amount of distortion primarily due to the amount of the heat input produced. The welder has little control on the heat input specified in a welding procedure. This does not prevent the welder from trying to minimize distortion. While the welder needs to provide adequate weld metal, the welder should not needlessly increase the total weld metal volume added to a weldment. Parent metal properties, which have an effect on distortion, are coefficient of thermal expansion and specific heat of the material. The coefficient of thermal expansion of the metal affects the degree of thermal expansion and contraction and the associated stresses that result from the welding process. This in turn determines the amount of distortion in a component. Weld joint design will effect the amount of distortion in a weldment. Both butt and fillet joints may experience distortion. However, distortion is easier to minimize in butt joints. Part fit up should be consistent to fabricate foreseeable and uniform shrinkage. Weld joints should be adequately and consistently tacked to minimize movement between the parts being joined by welding.Alloy SelectionBase metal and filler metal alloy selection is critical to producing good quality welds. Proper alloy selection can reduce numerous welding problems.Does the aluminum welding you are performing result in significant reductions in tensile strength? Is the alloy you are using susceptible to cracking.? Does your weld need a post welding heat treatment? Are your processing parameters appropriate? Can your yield be improved? Can your weld quality be improved? Contact us about exotic alloys or common alloys as listed below:Commonly used Welding Alloys Aluminum Steel Stainless Steel Titanium Nickel and Cobalt Magnesium CopperBenefits from Proper Alloy SelectionIncrease weld quality and yield Proper weld joint strength Good corrosion and oxidation resistance Reduction of weld and HAZ cracking Eliminate reheat cracking Eliminate stress corrosion cracking Eliminate lamellar tearing Improved weldability Optimize dissimilar metal jointsWelding Steel Alloys Steel Alloys can be divided into five groups Carbon Steels High Strength Low Alloy Steels Quenched and Tempered Steels Heat Treatable Low Alloy Steels Chromium-Molybdenum SteelsSteels are readily available in various product forms. To establish a proper welding procedure it is necessary to know the material properties of the steel being welded. The American Iron and Steel Institute defines carbon steel as follows:Steel is considered to be carbon steel when no minimum content is specified or required for chromium, cobalt, columbium [niobium], molybdenum, nickel, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 per cent; or when the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60. Carbon steels are normally classified as shown below.Low-carbon steels contain up to 0.30 weight percent C. The largest category of this class of steel is flat-rolled products (sheet or strip) usually in the cold-rolled and annealed condition. The carbon content for these high-formability steels is very low, less than 0.10 weight percent C, with up to 0.4 weight percent Mn. For rolled steel structural plates and sections, the carbon content may be increased to approximately 0.30 weight percent, with higher manganese up to 1.5 weight percent. Medium-carbon steels are similar to low-carbon steels except that the carbon ranges from 0.30 to 0.60 weight percent and the manganese from 0.60 to 1.65 weight percent. Increasing the carbon content to approximately 0.5 weight percent with an accompanying increase in manganese allows medium-carbon steels to be used in the quenched and tempered condition.High-carbon steels contain from 0.60 to 1.00 weight percent C with manganese contents ranging from 0.30 to 0.90 weight percent.High-strength low-alloy (HSLA) steels, or microalloyed steels, are designed to provide better mechanical properties than conventional carbon steels. They are designed to meet specific mechanical properties rather than a chemical composition. The chemical composition of a specific HSLA steel may vary for different product thickness to meet mechanical property requirements. The HSLA steels have low carbon contents (0.50 to ~0.25 weight percent C) in order to produce adequate formability and weldability, and they have manganese contents up to 2.0 weight percent. Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium, and zirconium are used in various combinations.Below are some typical welding considerations when welding carbon and low alloy steels Carbon Equivalent of the Steel Weld Cooling Rates Solidification Cracking Reheat Cracking Lamellar Tearing Hydrogen CrackingWelding Stainless Steel The stainless properties of stainless steels are primarily due to the presence of chromium in quantities greater than roughly 12 weight percent. This level of chromium is the minimum level of chromium to ensure a continuous stable layer of protective chromium-rich oxide forms on the surface. The ability to form chromium oxide in the weld region must be maintained to ensure stainless properties of the weld region after welding. In commercial practice, however, some stainless steels are sold containing as little as 9 weight percent chromium and will rust at ambient temperatures. Stainless steels are generally classified by their microstructure and are identified as ferritic, martensitic, austenitic, or duplex (austenitic and ferritic). The microstructure significantly affects the weld properties and the choice of welding procedure used for these stainless steel alloys. In addition, a number of precipitation-hardenable (PH) stainless steels exist. Precipitation-hardenable stainless steels have martensitic or austenitic microstructures.Iron, carbon, chromium and nickel are the primary elements found in stainless steels and significantly affect microstructure and welding. Other alloying elements are added to control microstructure or enhance material properties. These other alloys affect welding properties by changing the chromium or nickel equivalents and thereby changing the microstructure of the weld metal. Generally, 200 and 300 series alloys are mostly austenitic and 400 series alloys are ferritic or martensitic, but exceptions exist. Stainless steels are subject to several forms of localized corrosive attack. The prevention of localized corrosive attack is one of the concerns when selecting base metal, filler metal and welding procedures when fabricating components from stainless steels. Stainless steels are subject to weld metal and heat affected zone cracking, the formation of embrittling second phases and concerns about ductile to brittle fracture transition. The prevention of cracking or the formation of embrittling microstructures is another main concern when welding or fabricating stainless steels. Welding Austenitic Stainless SteelsIdeally, austenitic stainless steels exhibit a single-phase, the face-centered cubic (fcc) structure, that is maintained over a wide range of temperatures. This structure results from a balance of alloying additions, primarily nickel, that stabilize the austenite phase from elevated to cryogenic temperatures. Because these alloys are predominantly single phase, they can only be strengthened by solid-solution alloying or by work hardening. Precipitation-strengthened austenitic stainless steels will be discussed separately below. The austenitic stainless steels were developed for use in both mild and severe corrosive conditions. Austenitic stainless steels are used at temperatures that range from cryogenic temperatures, where they exhibit high toughness, to elevated temperatures, where they exhibit good oxidation resistance. Because the austenitic materials are nonmagnetic, they are sometimes used in applications where magnetic materials are not acceptable. The most common types of austenitic stainless steels are the 200 and 300 series. Within these two grades, the alloying additions vary significantly. Furthermore, alloying additions and specific alloy composition can have a major effect on weldability and the as-welded microstructure. The 300 series of alloys typically contain from 8 to 20 weight percent Ni and from 16 to 25 weight percent Cr. A concern, when welding the austenitic stainless steels, is the susceptibility to solidification and liquation cracking. Cracks can occur in various regions of the weld with different orientations, such as centerline cracks, transverse cracks, and microcracks in the underlying weld metal or adjacent heat-affected zone (HAZ). These cracks are primarily due, to low-melting liquid phases, which allow boundaries to separate under the thermal and shrinkage stresses during weld solidification and cooling.Even with these cracking concerns, the austenitic stainless steels are generally considered the most weldable of the stainless steels. Because of their physical properties, the welding behavior of austenitic stainless steels is different than the ferritic, martensitic, and duplex stainless steels. For example, the thermal conductivity of austenitic alloys is roughly half that of ferritic alloys. Therefore, the weld heat input that is required to achieve the same penetration is reduced. In contrast, the coefficient of thermal expansion of austenite is 30 to 40 percent greater than that of ferrite, which can result in increases in both distortion and residual stresses, due to welding. The molten weld pool of the austenitic stainless steels is commonly more viscous, or sluggish, than ferritic and martensitic alloys. This slows down the metal flow and wettability of welds in austenitic alloys, which may promote lack-of-fusion defects when poor welding procedures are employed.Welding Ferritic Stainless Steels Ferritic stainless steels comprise approximately half of the 400 series stainless steels. These steels contain from 10.5 to 30 weight percent chromium along with other alloying elements, particularly molybdenum. Ferritic stainless steels are noted for their stress-corrosion cracking (SCC) resistance and good resistance to pitting and crevice corrosion in chloride environments, but have poor toughness, especially in the welded condition. Ideally, ferritic stainless steels have the body-centered cubic (bcc) crystal structure known as ferrite at all temperatures below their melting temperatures. Many of these alloys are subject to the precipitation of undesirable intermetallic phases when exposed to certain temperature ranges. The higher-chromium alloys can be embrittled by precipitation of the tetragonal sigma phase, which is based on the compound FeCr. Molybdenum promotes formation of the complex cubic chi phase, which has a nominal composition of Fe36Cr12Mo10. Embrittlement increases with increasing chromium plus molybdenum contents. It is generally agreed that the severe embrittlement which occurs upon long-term exposure is due to the decomposition of the iron-chromium ferrite phase into a mixture of iron-rich alpha and chromium-rich alpha-prime phases. This embrittlement is often called "alpha-prime embrittlement." Additional reactions such as chromium carbide and nitride precipitation may play a significant role in the more rapid, early stage 885 °F embrittlement.The ferritic stainless steels have higher yield strengths and lower ductilities than austenitic stainless steels. Like carbon steels, and unlike austenitic stainless steels, the ferritic stainless alloys exhibit a transition from ductile-to-brittle behavior as the temperature is reduced, especially in notched impact tests. The ductile-to-brittle transition temperature (DBTT) for the ultrahigh-purity ferritic stainless steels is lower than that for standard ferritic stainless steels. It is typically below room temperature for the ultrahigh-purity ferritic stainless steels. Nickel additions lower the DBTT and there by slightly increase the thicknesses associated with high toughness. Nevertheless, with or without nickel, the ferritic stainless steels would need engineering review for anything other than thin walled applications as they are prone to brittle failure.Welding Martensitic Stainless Steels Martensitic stainless steels are considered to be the most difficult of the stainless steel alloys to weld. Higher carbon contents will produce greater hardness and, therefore, an increased susceptibility to cracking. In addition to the problems that result from localized stresses associated with the volume change upon martensitic transformation, the risk of cracking will increase when hydrogen from various sources is present in the weld metal. A complete and appropriate welding process is needed to prevent cracking and produce a sound weld.Martensitic stainless steels are essentially alloys of chromium and carbon that possess a body-centered cubic (bcc) or body-centered tetragonal (bct) crystal structure (martensitic) in the hardened condition. They are ferromagnetic and hardenable by heat treatments. Their general resistance to corrosion is adequate for some corrosive environments, but not as good as other stainless steels.The chromium content of these materials generally ranges from 11.5 to 18 weight percent, and their carbon content can be as high as 1.2 weight percent. The chromium and carbon contents are balanced to ensure a martensitic structure after hardening. Martensitic stainless steels are chosen for their good tensile strength, creep, and fatigue strength properties, in combination with moderate corrosion resistance and heat resistance. The most commonly used alloy within this stainless steel family is type 410, which contains about 12 weight percent chromium and 0.1 weight percent carbon to provide strength. Molybdenum can be added to improve mechanical properties or corrosion resistance. Nickel can be added for the same reasons. When higher chromium levels are used to improve corrosion resistance, nickel also serves to maintain the desired microstructure and to prevent excessive free ferrite. The limitations on the alloy content required to maintain the desired fully martensitic structure restrict the obtainable corrosion resistance to moderate levels.Welding Duplex Stainless SteelsDuplex stainless steels are two phase alloys based on the iron-chromium-nickel system. Duplex stainless steels usually comprise approximately equal proportions of the body-centered cubic (bcc) ferrite and face-centered cubic (fcc) austenite phases in their microstructure and generally have a low carbon content as well as, additions of molybdenum, nitrogen, tungsten, and copper. Typical chromium contents are 20 to 30 weight percent and nickel contents are 5 to 10 weight percent. The specific advantages offered by duplex stainless steels over conventional 300 series stainless steels are strength, chloride stress-corrosion cracking resistance, and pitting corrosion resistance.Duplex stainless steels are used in the intermediate temperature ranges from ambient to several hundred degrees Fahrenheit (depending on environment), where resistance to acids and aqueous chlorides is required. The weldability and welding characteristics of duplex stainless steels are better than those of ferritic stainless steels, but generally not as good as austenitic materials.A suitable welding process is needed to obtain sound welds. Duplex stainless steel weldability is generally good, although it is not as forgiving as austenitic stainless steels. Control of heat input is important. Solidification cracking and hydrogen cracking are concerns when welding duplex stainless steels, but not as significant for some other stainless steel alloys. Current commercial grades of duplex stainless steels contain between 22 and 26 weight percent chromium, 4 to 7 weight percent nickel, up to 4.5 weight percent molybdenum, as well as some copper, tungsten, and nitrogen. Modifications to the alloy compositions have been made to improve corrosion resistance, workability, and weldability. In particular, nitrogen additions have been effective in improving pitting corrosion resistance and weldability. The properties of duplex stainless steels can be appreciably affected by welding. Due to the importance of maintaining a balanced microstructure and avoiding the formation of undesirable metallurgical phases, the welding procedures must be properly specified and controlled. If the welding procedure is improper and disrupts the appropriate microstructure, loss of material properties can occur.Because these steels derive properties from both austenitic and ferritic portions of the structure, many of the single-phase base material characteristics are also evident in duplex materials. Austenitic stainless steels have good weldability and low-temperature toughness, whereas their chloride SCC resistance and strength are comparatively poor. Ferritic stainless steels have good resistance to chloride SCC but have poor toughness, especially in the welded condition. A duplex microstructure with high ferrite content can therefore have poor low-temperature notch toughness, whereas a structure with high austenite content can possess low strength and reduced resistance to chloride SCC. The high alloy content of duplex stainless steels also makes them susceptible to the formation of intermetallic phases from extended exposure to high temperatures. Significant intermetallic precipitation may lead to a loss of corrosion resistance and sometimes to a loss of toughness.Duplex stainless steels have roughly equal proportions of austenite and ferrite, with ferrite being the matrix. The duplex stainless steels alloying additions are either austenite or ferrite formers. This is occurs by extending the temperature range over which the phase is stable. Among the major alloying elements in duplex stainless steels chromium and molybdenum are ferrite formers, whereas nickel, carbon, nitrogen, and copper are austenite formers. Composition also plays a major role in the corrosion resistance of duplex stainless steels. Pitting corrosion resistance can be adversely affected. To determine the extent of pitting corrosion resistance offered by the material, a pitting resistance equivalent is commonly used.Welding Precipitation-Hardenable Stainless Steels Precipitation-hardening (PH) stainless steels are iron-chromium-nickel alloys. They generally have better corrosion resistance than martensitic stainless steels. The high tensile strengths of the PH stainless steels is due to precipitation hardening of a martensitic or austenitic matrix. Copper, aluminum, titanium, niobium (columbium), and molybdenum are the primary elements added to these stainless steels to promote precipitation hardening. Precipitation-hardening stainless steels are commonly categorized into three types martensitic, semiaustenitic, and austenitic based on their martensite start and finish (Ms and Mf) temperatures and the resulting microstructures. The issues involved in welding PH steels are different for each group. It is important to understand the microstructure of the particular type of alloy being welded. Some of the PH stainless steels solidify as primary ferrite and have relatively good resistance to hot cracking. In other PH stainless steels, ferrite is not formed, and it is more difficult to weld these alloys without hot cracking.Aluminum Welding Aluminum is the most difficult alloy to weld. Aluminum oxide should be cleaned from the surface prior to welding. Aluminum comes in heat treatable and nonheat treatable alloys. Heat treatable aluminum alloys get their strength from a process called ageing. Significant decrease in tensile strength can occurs when welding aluminum due to over aging. For more information on aluminum welding processes, benefits of welding processes, welding discontinuities, or common welding problems please visit our homepage or any of the links to your left. Take advantage of our aluminum welding experience in developing your welding processes.Aluminum Alloys can be divided into nine groups: 1xxx Unalloyed (pure) >99% Al 2xxx Copper is the principal alloying element, though other elements (Magnesium) may be specified 3xxx Manganese is the principal alloying element 4xxx Silicon is the principal alloying element 5xxx Magnesium is the principal alloying element 6xxx Magnesium and Silicon are principal alloying elements 7xxx Zinc is the principal alloying element, but other elements such as Copper, Magnesium, Chromium, and Zirconium may be specified 8xxx Other elements (including Tin and some Lithium compositions) 9xxx Reserved for future useAluminum alloys are readily available in various product forms. To establish a proper welding procedure it is necessary to know the material properties of the Aluminum alloy being welded. Below are some of the factors affecting the welding of Aluminum.Aluminum Oxide CoatingThermal Conductivity Thermal Expansion Coefficient Melting CharacteristicsWrought Aluminum Alloys 1xxx Series. These grades of aluminum are characterized by excellent corrosion resistance, high thermal and electrical conductivities, low mechanical properties, and excellent workability. Moderate increases in strength may be obtained by strain hardening. Iron and silicon are the major impurities. 2xxx Series. These alloys require solution heat treatment to obtain optimum properties; in the solution heat-treated condition, mechanical properties are similar to, and sometimes exceed, those of low-carbon steel. In some instances, precipitation heat treatment (aging) is employed to further increase mechanical properties. This treatment increases yield strength, with attendant loss in elongation; its effect on tensile strength is not as great. The alloys in the 2xxx series do not have as good corrosion resistance as most other aluminum alloys, and under certain conditions they may be subject to intergranular corrosion. Alloys in the 2xxx series are good when some strength at moderate temperatures is desired. These alloys have limited weldability, but some alloys in this series have superior machinability. 3xxx Series. These alloys generally are non-heat treatable but have about 20% more strength than 1xxx series alloys. Because only a limited percentage of manganese (up to about 1.5%) can be effectively added to aluminum, manganese is used as a major element in only a few alloys. 4xxx Series. The major alloying element in 4xxx series alloys is silicon, which can be added in sufficient quantities (up to 12%) to cause substantial lowering of the melting range. For this reason, aluminum-silicon alloys are used in welding wire and as brazing alloys for joining aluminum, where a lower melting range than that of the base metal is required. The alloys containing appreciable amounts of silicon become dark gray to charcoal when anodic oxide finishes are applied and hence are in demand for architectural applications. 5xxx Series. The major alloying element is Magnesium and when it is used as a major alloying element or with manganese, the result is a moderate-to-high-strength work-hardenable alloy. Magnesium is considerably more effective than manganese as a hardener, about 0.8% Mg being equal to 1.25% Mn, and it can be added in considerably higher quantities. Alloys in this series possess relatively good welding characteristics and relatively good resistance to corrosion in marine atmospheres. However, limitations should be placed on the amount of cold work and the operating temperatures permissible for the higher-magnesium alloys to avoid susceptibility to stress-corrosion cracking. 6xxx Series. Alloys in the 6xxx series contain silicon and magnesium approximately in the proportions required for formation of magnesium silicide (Mg2Si), thus making them heat treatable. Although not as strong as most 2xxx and 7xxx alloys, 6xxx series alloys have relatively good formability, weldability, machinability, and relatively good corrosion resistance, with medium strength. Alloys in this heat-treatable group are sometimes formed in the T4 temper (solution heat treated but not precipitation heat treated) and strengthened after forming to full T6 properties by precipitation heat treatment. 7xxx Series. Zinc, in amounts of 1 to 8% is the major alloying element in 7xxx series alloys, and when coupled with a smaller percentage of magnesium results in heat-treatable alloys of moderate to high strength. Usually other elements, such as copper and chromium, are also added in small quantities. Some 7xxx series alloys have been used in airframe structures, and other highly stressed parts. Higher strength 7xxx alloys exhibit reduced resistance to stress corrosion cracking and are often utilized in an overaged temper to provide better combinations of strength, corrosion resistance, and fracture toughness.